The present invention relates to an improved interlayer product for the preparation of laminated safety glass. More particularly, the invention relates to an interlayer product for laminated safety glass whereby multiple layers of interlocking interlayer film having the desired properties of thickness and melt fracture surface pattern are combined to meet a specific functional need.
In laminated safety glass used for window glass for buildings and such, it is not uncommon for the laminator to use thicker interlayer than typically used in automotive applications, which is nominally 0.76 mm (30 mils) thick, or to combine multiple layers of 0.76 mm (30 mils) interlayer to achieve a thicker product for enhanced structural properties. There is, however, no disclosure of the manufacture or use of interlocking layers (at least two)of polyvinyl butyral containing film between layers of glass.
The extrusion process for the production of thick interlayer, that is greater than 0.76 mm (30 mils), requires high throughput rates and low line speeds, and results in deficiencies in dimensional stability, such as shrinkage, difficulty in winding and cutting, and additional manufacturing transitions and problems in generating the melt fracture surface pattern necessary for proper de-airing when laminating the glass/interlayer construction.
It has now been found that by combining, in a controlled winding process, at least two layers of interlayer of varying thickness with the desired melt fracture surface pattern in such a way that sufficient interlocking of the sheets occurs, excellent glass laminates are achieved. When unwound, the sheets may be handled as an integral unit but are not so intimately bonded that air will be trapped between the layers which will result in an unacceptable glass laminate.
U.S. Pat. No. 4,230,771 describes polyvinyl butyral laminates with tetraethyleneglycol di-N-heptanoate plasticizer. This patent specifically discloses a sheeting of polyvinyl butyral and plasticizer which was formed into a single sheeting of 0.80 mm laminated between two layers of glass. There is no teaching of multiple layers of polyvinyl butyral of any thickness.
U.S. Pat. No. 4,292,372 discloses polyvinyl butyral sheeting plasticized with a hydrolyzable ester having low acid concentration. This reference disclose a sheet of 0.03 inches which was laminated between two sheets of glass.
U.S. Pat. No. 4,297,262 describes polyvinyl butyral plasticized with tetraethyleneglycol di-n-heptanoate. The references describes the use of a single sheet of such material sandwiched between layers of glass to provide a composite material resistant to shattering.
European Patent EP 0 710 545 describes a multi-layer product for laminated glass whereby the multi-layer elements are first intimately bonded and then the desired pattern embossed upon the outer surfaces. Further, it is pointed out that if the outermost layer is not thick enough, minute disruptions occur at the interface which lead to optical distortion. The layers may consist of different plasticized polyvinyl butyral resin films having different average degrees of polymerization (delta 300-4,500) and/or having different plasticizer percentages or content (delta=5 weight parts to 50 weight parts per 100 parts of the resin which makes up each interlayer). Other differences between interlayers include films with different glass transition temperatures, etc.
In the present invention, even with pattern on both surfaces of the interface, optical distortion is not observed.
European Patent, EP 0 465 698 A1, describes a process for integrally ply-bonding two webs of paper.
In the process of the present invention, two or more rolls of sheeting comprising polyvinyl butryal as the primary component with plasticizers as the secondary component as interlayer and/or interleaving material are simultaneously unwound and rewound together under controlled tension, line speed and temperature so that the edges of the respective layers are aligned and roll fonnation is normal, the tension on the respective sheets is equal, thickness is maintained and entrapped air is minimized. The resulting product is used to produce laminated safety glass with thick interlayer construction.
The present invention therefore comprises a multilayer composite structure, comprising, in order,
(a) a first layer of plasticized polyvinyl butryal; and
(b) one or more additional layers of plasticized polyvinyl butryal wherein layers (a) and (b) are interlocked. This multilayer composite The present invention relates to an interlayer product for laminated safety glass whereby multiple layers of interlocking interlayer film having the desired properties of thickness and melt fracture surface pattern are combined to meet a specific functional need. In the present invention, two or more rolls of sheeting comprising polyvinyl butyral as the primary component are simultaneously unwound and rewound together under controlled tension, line speed and temperature so that the edges of the respective layers are aligned and roll formation is normal, the tension on the respective sheets is equal, thickness is maintained and entrapped air is minimized. The resulting product is used to produce laminated safety glass with thick interlayer construction structure is useful as a material which is sandwiched between layers or multiple layers of glass to form shatter resistant glass composite structures for use in automobile windows, commercial windows and the like. More particularly, the present invention comprises said multilayer composite structure wherein the first layer and the one or more additional layers are equal to or greater than 0.38 mm per layer. The preferred system or preferred multilayer plasticized polyvinyl butryal layers have either the same degree of polymerization of PVB or the same percentage of plasticizer in each layer relative to the weight of the PVB in that layer or both the same degree of polymerization and the same percentage of plasticizer.
The present invention further relates to or comprises a process for producing the multilayer composite structure described above by,
(i) unwinding a first layer of plasticized polyvinyl butyral from a first roller (1xe2x80x2) at a line speed of 10-50 meters/min. and at a temperature of 5-35xc2x0 C. and at an unwind tension of 4-70 Newton meter/meter of sheet width to form a first web;
(ii) simultaneously unwinding at least one additional layer of plasticized polyvinyl butyral from a second roller (1) at a line speed of 10-50 meters/min. and at a temperature of 5-35xc2x0 C. and at an unwind tension of 4-45 Newton meter/meter of sheet width to form at least a second web; and
(iii) combining layers (i) and (ii) on a windup roller (5) to form an aligned interlocked multilayer composite structure.
Thus, PVB sheeting between 15 and 60 mils (0.38 mm to 1.52 mm) may be utilized with the tension varying accordingly. The process may further comprise unwinding a protective sheet of polyolefin from an unwind roller (1xe2x80x3) at a tension of 2 to 5 Newton meter/meter simultaneously with the first and second rollers and, in step (3), combining layers (i) and (ii) with the protective sheet as the top layer on the windup roller (5) to form an aligned interlocked multilayer composite structure having a protective sheet of polyolefin.
The present invention further relates to a multilayer composite structure produced from the process(es) recited above.
The present invention also relates to a multilayer composite structure, comprising, in order,
(a) at least one glass layer;
(b) at least two interlocking layers of plasticized polyvinyl butyral; and
(c) at least one additional glass layer and relates to said multilayer composite structure produced by (i) forming at least two interlocking layers of plasticized polyvinyl butyral and (ii) sandwiching the at least two interlocking layers between glass layers (a) and (b) wherein the interlocking layers before step (ii) have not been exposed to ambient temperatures greater than 10xc2x0 C.